DESCRIPTION: Issues of size and scale affect human communication, thought, and inquiry in many ways. For example, in the sciences, changes in conceptions of size and scale have had dramatic effects on the development of many core ideas. In biology, for example, the invention of the microscope made accessible a different scale of biological function. This discovery altered fundamentally conceptions of life and reproduction. The effects of changes in conceptions of scale relations might also affect children's thinking in analogous ways. Consequently, the development of children's comprehension of scale relations is an issue of substantial importance. The long term goal of the proposed research is to develop an account of how young children come to understand and use scale relations. The proposed research consists of a set of psychological experiments that are designed to be meaningful to young children. The proposal addresses two reciprocal aims. The first specific aim is to develop and test elements of an account of the development of children's understanding and use of scale relations in a specific domain, spatial cognition. Spatial tasks provide an ideal domain in which to investigate children's conception of scale relations. For example, understanding and using scale information is of critical importance to many aspects of spatial cognition, including the coordination of perspectives and the use of maps and scale models. In addition, spatial tasks are motivating and interesting for young children and have often been used to investigate the early development of many important cognitive skills. The second specific aim is to use children's performance in the scaling tasks as a window for studying the development of children's mental representations of spatial information. Scaling tasks may require that children mentally represent and systematically transform a set of spatial relations, and the ability to do this is an important milestone in the development of spatial cognition. This proposal introduces a theoretical perspective that focuses on how maps and scale models may help children (and adults) acquire information about the relations among objects in space. In addition, the results may be relevant to understanding neurological disorders, such as visual neglect and spatial agnosia, that affect the processing of spatial information. Taken together, the proposed studies would provide new information about an important, but relatively unexplored issue, the development of children's conception of scale relations. At the same time, the research would shed new light on a classic issue in cognitive development: the development of children's mental representations of spatial information.